Brick and stone walls are - as it is termed - covered by "two" or "three" coat work, consisting of a rendering or pricking up coat, a floating and a setting coat.
The first consists in covering the walls roughly with the patent materials specified, or with the coarse stuff (otherwise called " hair mortar") in common and ordinary work, consisting of the properly slaked fat lime, mixed wet with about three parts of good, clean, sharp, washed sand, and a proportion of good well-beaten cow-hair. This mixture is then applied to the walls, to the thickness of about 1/2 an inch, or as may be required to make the wall surface perfectly plumb and level. So soon as the coat begins to dry it is scored over or scratched to give the next or floating coat a key or means of attachment.
When this first - rendering or pricking-up - coat has become dry, the second ox floating coat is applied on it to a certain thickness, of from 1/8 to 1/4 of an inch. This coat consists of a better and stronger mixture of the same materials as the first, but with less hair, called "fine stuff." The surface of this coat is made truly even in every way following on the last by means of perfectly plumb, vertical, and horizontal screeds, laid on the walls to the required thicknesses, and about 6 inches wide, at the angles, ceiling, and skirting, and intermediately, as the straight edges, with which the spaces between are regulated, require.
This second coat is left rough from the float, as the tool used is called; and when it becomes dry the third or setting coat is applied, consisting of a very thin film of fine stuffy - i.e., "putty", or slaked lime, with a very small admixture of sand, made to about the consistency of good cream. This is applied and worked up to a perfectly smooth and level fare, which sets quite hard; after which it is left to dry, and the work is complete.
When a wall is intended to be painted it is finished with a trowelled face (for which purpose various other special plasters are sometimes used, to give it a better hardened face), the workman using a steel "trowel" for this purpose, instead of the wooden one, called a "float."
Two-coat work consists of an amalgamation of the first two coats, finished off with the setting coat.
Walls are sometimes battened; that is to say, thin battens are fixed to plugs, vertically up the walls at about 16 inches, centre to centre, to receive the lath-work (Fig. 881), as will be explained for partitions and ceilings. This "battening" is used for damp walls; but, while it gives a free circulation of air behind the plastering, it brings with it a greater evil, inasmuch as, besides being subject to decay, it forms a harbour for all kinds of vermin; and rooms with battened walls are made quite lively by the noise of mice and other such creatures. For the same reasons walls behind skirtings, etc., should be rendered up. In elevation, lathwork on battens looks exactly like lathwork on partitions or ceilings; the only difference appearing in the plans or sections, which in this instance are represented by Fig. 883.
Counter-lathing or brandering is similar to the above, and consists of ordinary laths laid about 16 inches apart on wood lintels, etc., to throw out the laths so as to allow of a key for the plaster work laid on them, over doors and windows and other openings spanned by wood, to which ordinary plastering will not adhere.
Ceilings and partitions, battening, and counter!athing are treated as tig. 881, Fig. 882 being a plan of the partition; and the work is specified, for two-coat work as lath, plaster, and set, or lath, float, and set, and for three-coat work as lath, plaster, float, and set, consisting of the same proceedings in laying on the material as for walls, with the "addition" of the "lathwork," which means the covering of the surfaces with laths of various thickness (as previously described) nailed to the framing at about 16 inches from centre to centre; the laths being parallel to one another, and about 3/8 of an inch apart, to allow of a key to the pricking-up or first coat of the plastering, which is pressed on to the lath and through the crevices to form a key. The laths are in various lengths up to 4 feet to suit the spaces of the wood framing; and where a joint is necessary it should not be perfectly vertical up the wall on the same piece of wood, but they should break joint every half-dozen laths, and so on, as Fig. 881. "Lath and half" are the best to use for ordinary work.
This lathing being done, the plastering is laid on exactly the same as on the walls, but it should be pointed out that the first coat takes much longer to dry, having no absorption to assist the drying process on laths, as is the case on walls.
All external angles should be roughed up either in Portland or Keene's cement, to make a good hard finish, as ordinary "hair-mortar" and "putty" have no strength for such positions; or "wood angle-beads" should be fixed to plugs in the joint, up the angle, and the plastering quirked up to it, as explained under "Joinery" (Chapter XVI (Joints And Mouldings In Joinery. Joinery Defined).).
When requisite, the plastering to walls, ceilings, partitions, etc., as above, can be made to dry quicker by the addition of a proportion (about one-fifth) of "plaster-of-Paris" to the ordinary mixtures for the various coats; and this is called gauged work. The proportion of plaster regulates the time of setting; but it is unadvisable to hurry the work of plastering, and certainly not by "gauging," which is apt in time to cause the whole surface to crack, almost like a spider's web.